Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. A typical knee prosthesis includes a tibial component, a femoral component, a femoral stem assembly, and a patellar component. The femoral component generally includes a pair of spaced apart condylar portions, the superior surfaces of which articulate with a portion of the tibial component. The femoral stem assembly provides lateral stability, and it typically includes a member that is inserted within a reamed intramedullary canal at the distal end of a femur. The stem is typically coupled to the femoral component by a collar and bolt through a bore or opening which extends completely through the femoral component.
Although modular systems can provide an advantageous reduction in joint component inventory, known systems do not fully address the problems associated with variations in intramedullary canal geometry. Specifically, the variations in the morphology of the intermedullary canal often do not match the geometry of the stem, forcing the surgical positioning of the femoral component that is mated to the stem to be determined by considerations other than the shape of the canal.
For example, if the implant geometry does not match the canal geometry, the stem of the implant can contact the cortical wall of the intramedullary canal while the stem is being impacted. This problem can be further complicated when a femoral stem is mated to a sleeve that increases the effective length of the stem so that it is in a bowed portion of the intramedullary canal.
In response to the above problems, a surgeon may be forced to remove the stem (or entire component) and replace it with a stem having a smaller diameter or shorter length, even if the replacement stem is thought to be less suitable than the original stem, but for the improper fit. Also, the surgeon may have to cut notches in the femur to accommodate a shifted femoral component.
Furthermore, known prosthesis attachment systems can cause additional problems related to the production of wear debris and third body particulates. Since known systems employ a stem which is typically attached to the femoral component through a bore which extends completely through the femoral component, any wear debris or particulates produced are able to easily migrate into the joint. The phenomenon of wear debris within artificial joints is a serious problem that can inhibit the proper mechanical functioning of the joint. If wear debris develops within an artificial joint, it must usually be corrected by surgical removal of the debris or by subsequent replacement of the artificial joint.
Therefore, despite the existence of joint prostheses having modular components, there remains a need for a modular joint prosthesis that has greater versatility to accommodate differing patient anatomy and joint conditions and reduces the possibility of wear debris and particulate migration and production.